sccache-dist / icecream preprocess the file and then send it to a builder.
That means that the file contains #line directives or equivalents in order for
diagnostics and such to work correctly.
Unfortunately our clang-plugin build fails catastrophically if you include a
third-party header, as it doesn't account for them.
Use SourceManager::getPresumedLoc to get filenames, as it accounts for them,
unlike just getFilename.
Differential Revision: https://phabricator.services.mozilla.com/D50633
--HG--
extra : moz-landing-system : lando
